Low friction means for sewing machine work clamp

ABSTRACT

A mechanism for minimizing frictional resistance to movement of sewing machine work clamps which permits a substantial increase in machine speed. Plastic lined sockets carrying steel ball bearings are elevated through the throat plate in timed relationship with the sewing needle rise and prior to feeding work clamp movement. The balls impinge on the bottom work clamp raising the bottom work clamp and upper work clamp out of engagement with the throat plate thereby also increasing clamping pressure on the work material between the clamps. An arched clamp frame which supports the work clamps absorbs the reaction force through similar balls in plastic lined sockets impinging on a hardened steel plate on the underside of the bracket arm. Motion of the entire clamp assembly takes place on ball bearings which are retracted during needle penetration to obviate flagging of the work material.

United States Patent Kostenowczyk LOW FRICTION MEANS FOR SEWING MACHINEWORK CLAMP [75] Inventor: Stanley Kostenowczyk, Cranford,

[73] Assignee: The Singer Company, New York,

[22] Filed: Oct. 4, 1974 [21] Appl. No.: 512,795

[52] US. Cl. 112/70 [51] Int. Cl. D05b 3/04 [58] Field of Search 112/70,76, 77, 65, 73, 112/74, 75, 218

[56] References Cited UNITED STATES PATENTS 2,822,771 2/1958 Hale et a1.ll2/65 3,824,938 7/l974 Tolle ll2/7O Primary Examiner-H. Hampton HunterAttorney, Agent, or Firm-Marshall .l. Breen; Edward L. Bell; Robert E.Smith [57] ABSTRACT A mechanism for minimizing frictional resistance tomovement of sewing machine work clamps which permits a substantialincrease in machine speed. Plastic lined sockets carrying steel ballbearings are elevated through the throat plate in timed relationshipwith the sewing needle rise and prior to feeding work clamp movement,The balls impinge on the bottom work clamp raising the bottom work clampand upper work clamp out of engagement with the throat plate therebyalso increasing clamping pressure on the work material between theclamps. An arched clamp frame which supports the work clamps absorbs thereaction force through similar balls in plastic lined sockets impingingon a hardened steel plate on the underside of the bracket arm. Motion ofthe entire clamp assembly takes place on ball bearings which areretracted during needle penetration to obviate flagging of the workmaterial.

5 Claims, 4 Drawing Figures -YIIIIIIIIIIIIIIIIIIIIIIL Q l- LOW FRICTIONMEANS FOR SEWING MACHINE WORK CLAMP BACKGROUND OF THE INVENTION Workclamps are customarily used on industrial sewing machines, such as bartackers and the like which are cyclic in nature; i.e. start,automatically perform a complete operation, and stop. Thus cyclic sewingmachines are designed to repetitively perform a specific function suchas attachment of a belt loop, button sewing, buttonholing or pocketsetting, for example. Generally work clamps are used to insure the mostaccurate stitching with the least operator attention therebysubstantially decreasing possibility for error.

Work clamps function to hold work material between a lower work clampimmediately adjacent the sewing machine throat plate, and an upper,spring loaded, work clamp. Both clamps are supported by an arched clampframe which is urged by a cam to pass through the cyclic motionrequired.

Present cyclic sewing machines are limited in speed of operation due inone respect to the friction between the lower work clamp and the throatplate. As the speed is increased the tacks produced by the machinebecome non-uniform and non-repetitive due to friction and frictionalchanges. The friction also generates forces severely stressing some ofthe parts further contributing to the non-uniformity. Thus bar tackershave required limitation in top speed to about 2,000 stitches per minutein order to insure uniformity of product.

Attempts to circumvent the problem by adding a teflon coating to certaincritical parts, or by giving these parts a highly polished finish havenot been sufficient to increase machine speed to enable greaterproduction. Also lubrication of the critical parts is not desirable inas much as the proximity of the work material to these parts gives riseto soiling of the work material by the lubricant.

In the prior art, attempts to improve friction by the use of bearingswhich are permanently effective have given rise to increased flagging ofthe work beneath the sewing needle as well as greater soiling ofmaterial adjacent lubricated parts.

What is required is some means of reducing the friction on the workclamp sufficiently to allow a substantial increase in speed withoutsacrificing clamp mobility or creating a problem of soiling of the workmaterial.

SUMMARY OF THE INVENTION The desired ends are obtained by this inventionin which plastic lined sockets carrying ball bearings are elevatedthrough the throat plate beneath the work clamps as the sewing needle iselevated. The work clamps are supported in the sewing machine by anarched clamp frame which transports the work clamp as directed by a camin the sub-bed of the sewing machine. The arched clamp frame supports aleaf spring used to press the upper work clamp against the lower workclamp to trap fabric therebetween; and thereby also presses the lowerwork clamp against the sewing machine throat plate. Reaction to thepressure of the work clamp against the throat plate, or against the ballbearings carried in the plastic lined sockets elevated through thethroat plate, is accommodated by similar ball bearings carried inplastic lined sockets supported on top of the arched clamp frame. Theupper ball bearings impinge on a hardened steel plate carried on theunderside of the sewing machine bracket arm.

The invention comprises the devices, combinations and arrangement ofparts hereinafter described and illustrated in the accompanying drawingsof a preferred embodiment in which:

FIG. 1 is a front side elevational view, partly in cross section, ofasewing machine embodying the present invention;

FIG. 2 is a cross sectional view taken substantially along the line 22in FIG. 1;

FIG. 3 is sectional view of the ball bearing and plastic socket to showdetails of construction; and

FIG. 4 is a cross sectional view taken substantially along the line 44in FIG. 2.

In FIG. 1 is shown a sewing machine having a bracket arm 11, terminatingin a head 12, projecting from an arm standard 13.

The arm standard 13 depends from a sub-base 15, as

I does a work supporting bed 16, having a work supporting throat plate17.

Extending through the bracket arm 11 is a main shaft to which is affixeda drive pulley 21. Not shown is the conventional mechanism used to drivea needle bar 23 and a sewing needle 24 affixed to the end thereof. Abelt 25 connects the drive pulley 21 to a hook shaft drive pulley 26affixed to a hook drive shaft 27 located in the bed 16 of the sewingmachine. A hook 28 located on the end of the hook drive shaft 27opposite the hook drive shaft pulley 26 cooperates with the needle 24 inthe formation of lock stitches. To achieve this end the drive pulley 21and the hook drive shaft pulley 26 are in the ratio of 2 to 1 that thehook drive shaft 27 and the hook 28 affixed thereto rotate at twice thespeed of the main shaft 20 and needle 24 operatively connected thereto.

Beneath the bracket arm 11 may be noted a work clamp mechanism thedetails of which are set out in great particularity in the U.S. Pat. No.2,822,771, issued on Feb. 11, 1958 to A. N. Hale et al. which patent ishereby incorporated by reference and made a part of this application.The work clamps will be described only insofar as is pertinent andrequired to the disclosure of the instant invention.

Referring to FIG. 1, the work clamp assembly includes an arched clampframe 30 attached by screws 31 to a base portion 32 supported on the bed16. The base portion 32 and arched clamp frame 30 are urged to motion,in synchronism with sewing needle 24 retraction from the work fabric, bycam followers 35, 36 impelled by cam tracks 37, 38 in the cam 40 locatedin the subbase 15 of the sewing machine 10. The cam 40 is carried bygear 41 which is driven by drive gear 42 operatively connected to thesewing machine main shaft 20.

Depending from the arched clamp frame 30 by a shank portion 45 is anupper work clamp 46. A leaf spring 48 impinges on the extension of theshank portion 45 through the arched clamp frame 30 in a fashion to urgethe upper work clamp 46 towards the bed 16. An adjusting screw 49 bearson the leaf spring 48 to increase or decrease the force exerted on theshank portion 45 of the upper work clamp 46. A projecting stud 50 isinterengaged with the shank portion 45 to elevate the shank portion 45and the upper work clamp 46 against the urgings of the leaf spring 48,whenever an angle bracket 51, affixed to a presser lifter mechanism,

is elevated by the presser lifter mechanism to a position where it willstrike and lift the projecting stud.

Attached to the free extremity of the base portion 32 by screws is alower work clamp 56. In its needle penetration position the lower workclamp 56 is supported by the throat plate 17. Work material is claspedbetween the upper work clamp 46 and the lower work clamp 56 and, underthe urging of the leaf spring 48, both clamps and work material arepressed against the throat plate 17, a position designed to avertflagging of the work material.

Located in the work supporting bed 16 and supported on bearings thereinis a lift shaft 60. A drive gear 61 affixed to the hook drive shaft 27meshes with a lift shaft gear 63 attached to an extremity of the liftshaft 60. The gears are in a ratio of l to 2 so that, in view of the 2to 1 ratio of the drive pulley 21 to the hook shaft pulley 26, the liftshaft is running at the same speed as the main shaft 20.

On the extremity of the lift shaft 60 opposite the lift shaft gear 63 isa hole, eccentric to the shaft center line, into which is inserted andheld by set screw 64 a headed pivot pin 65, thereby forming a crank.Rotatably supported on the pivot pin 65 is a lift shaft connecting link66 (see also FIG. 2). The lift shaft connecting link 66 is formed on theend opposite that accommodating the pivot pin 65 with a pair of slots 68receiving levers 70 for oscillation about a pin 71 fast to the shaftlink. The levers 70 are centrally pivoted on adjustment pins 74 held byset screws 75 to an adjusted position in the bed 16. The adjustment pins74 are used for adjustment purposes as will be explained below and areformed with an eccentric shaft extension portion held fast by the setscrews 75 to the bed 16. Thus as the pins 74 are revolved in the bed 16by means of screw driver slots 76, the inclination of the levers 70about the pin 71 varies. When the adjusted position is reached the setscrew 75 may be seated against the adjustment pin to maintain thatspecific setting.

To the ends of the levers 70 opposite that oscillatable about pin 71,the levers are pivotably attached to push rods 83 which extend upwardlyon either side of the rotating hook shaft (see FIG. 2). Pivotablysupported on the ends of the push rods 83 are bearing means 85 (see FIG.4) having a cup shaped end 86 receiving a molded or fabricated lowfriction synthetic resin polymer 87 fashioned with a socket 88 toreceive a ball 90. Most ideally the synthetic resin polymer used wouldbe poly tetra fluoro ethylene or a substantial equivalent thereof. Theball utilized must be of a sufficient diameter to preclude formation ofa depression in the Synthetic resin polymer used, for the loadsupported.

As can be noted in FIG. 2 the balls 90 protrude through the throat plate17 an amount adjustable by manipulation of the adjustment pins 74.Referring to FIG. 1 the balls protrude through the throat plate 17beneath the lower work clamp 56, lifting it and the upper work clamp 46against theurgings of the leaf spring 48.

Attached to the underside of the bracket arm 11 above the arched clampframe 30 is a race plate of hardened steel material. Supported by thearched clamp frame 30 are second bearing means 97 receiving molded orfabricated inserts 98 of synthetic resin polymer, preferably poly tetrafluoro ethylene. The inserts are formed with sockets 99 for receivingballs 100. By means of an adjusting screw 101 clearance between theballs 100 and the race plate 95 may be taken up. and the position thusachieved locked by nut 102.

Thus for the sliding friction heretofor encountered on those memberssubject to clamping pressure is substituted rolling friction. Asynthetic resin polymer is used which has very low friction propertiesand whose static coefficient of friction is the same as its dynamiccoefficient of friction. These changes have enabled the top speed of thesewing machine to increase from a maximum 2,000 s.p.m. to 4,000 s.p.m.Although only two balls have been shown elevating the lower work.

clamp 56 it is obvious that this principle is expandable to encompassadditional balls, or may even be utilized to elevate an entire worksupporting surface for low friction transport.

Experience has shown that lowering of the work clamp during workpenetration by the needle is re quired to prevent flagging of the work.Flagging is caused by passage of the sewing needle through poorlysupported fabric causing the work material to deflect. If the balls 90of this invention were to remain elevated continuously, flagging mightresult with subsequent deleterious effect on loop formation resulting ina skipped stitch. For this reason the mechanism of this invention isrequired.

Having thus set forth the nature of the invention, what I claim is:

1. In a sewing machine having a frame, a sewing needle, means forreciprocating said sewing needle upwardly out of work material anddownwardly through work material, said frame including a bed with anaperture for accommodating said reciprocation of said sewing needle,work clamp means for supporting and transporting work material on saidbed, said work clamp means including an upper clamp member and a lowerclamp member, and means for supporting and transporting said work clampmeans when said sewing needle is out of work material, the improvementcomprising: at least one ball and bearing means effective between saidbed and said work clamp means, said bearing means including a socket forreceiving said ball;

means for shifting said bearing means to position said ball in a spacebetween said bed and said work clamp means lower clamp member insynchronism with said upward needle reciprocation to elevate said workclamp means by said ball impinging on said lower clamp member prior totransport of said work clamp means.

2. In a sewing machine as claimed in claim 1 wherein said socket of saidbearing means is formed of a low friction synthetic plastic resin.

3. In a sewing machine as claimed in claim 2 wherein said means forsupporting and transporting said work clamp means includes an archedclamp frame, resilient means supported on said arched clamp frame and inoperative connection with said upper clamp member of said work clampmeans urging said work clamp means into contact with said sewing machinebed, and at least one ball and bearing means between said arched clamp Iframe and said sewing machine frame whereby reaction force of saidresilient means is transferred to said sewing machine frame through saidlost mentioned at least one ball and bearing means.

4. In a sewing machine as claimed in claim 3 wherein said means forelevating said ball and bearing means includes a crank revolving insynchronism with said needle reciprocations, a connecting link havingone end pivotably connected to said crank, a lever pivotably connectedto the other end of said connecting link, said lever itself pivotablyconnected to said frame, a push rod having one end pivotably connectedto said lever, said push rod having its other end pivotably connected tosaid bearing means whereby said bearing means is elevated through saidbed in synchronism with said upward needle reciprocation.

5. In a sewing machine having a frame including a work supporting bed,work clamp means including an upper clamp member and a lower clampmember, intermittently operative means for transporting said work ingtransport of said work clamp means.

1. In a sewing machine having a frame, a sewing needle, means forreciprocating said sewing needle upwardly out of work material anddownwardly through work material, said frame including a bed with anaperture for accommodating said reciprocation of said sewing needle,work clamp means for supporting and transporting work material on saidbed, said work clamp means including an upper clamp member and a lowerclamp member, and means for supporting and transporting said work clampmeans when said sewing needle is out of work material, the improvementcomprising: at least one ball and bearing means effective between saidbed and said work clamp means, said bearing means including a socket forreceiving said ball; means for shifting said bearing means to positionsaid ball in a space between said bed and said work clamp means lowerclamp member in synchronism with said upward needle reciprocation toelevate said work clamp means by said ball impinging on said lower clampmember prior to transport of said work clamp means.
 2. In a sewingmachine as claimed in claim 1 wherein said socket of said bearing meansis formed of a low friction synthetic plastic resin.
 3. In a sewingmachine as claimed in claim 2 wherein said means for supporting andtransporting said work clamp means includes an arched clamp frame,resilient means supported on said arched clamp frame and in operativeconnection with said upper clamp member of said work clamp means urgingsaid work clamp means into contact with said sewing machine bed, and atleast one ball and bearing means between said arched clamp frame andsaid sewing machine frame whereby reaction force of said resilient meansis transferred to said sewing machine frame through said lost mentionedat least one ball and bearing means.
 4. In a sewing machine as claimedin claim 3 wherein said means for elevating said ball and bearing meansincludes a crank revolving in synchronism with said needlereciprocations, a connecting link having one end pivotably connected tosaid crank, a lever pivotably connected to the other end of saidconnecting link, said lever itself pivotably connected to said frame, apush rod having one end pivotably connected to said lever, said push rodhaving its other end pivotably connected to said bearing means wherebysaid bearing means is elevated through said bed in synchronism with saidupward needle reciprocation.
 5. In a sewing machine having a frameincluding a work supporting bed, work clamp means including an upperclamp member and a lower clamp member, intermittently operative meansfor transporting said work clamp means, resilient means for urging saidwork clamp means against said bed and against work material interposedbetween said upper and said lower clamp members, wherein the improvementcomprises; a. a ball and socket bearing means b. means shiftablysupporting said ball and socket bearing means in said work supportingbed for movement intermittently against said lower clamp member intoopposition to said resilient means during transport of said work clampmeans.